MY first thought was rabies, but after reading what you just said, sounds more like poisoning. Chances are your neighbor had something like rat poison or antifreeze somehwhere. I'm sorry I don't have very good advice for you. If you're on good terms with your neighbor, you could try asking him he has any rat/fly poison out, or any chemicals and antifreeze anywhere in his yard your dog might of got into. Once you know what your dog got into, you can google it and perhaps find a cure. One other possibility is that your dog bit a toad. That will make him sick, but he should get better on his own if thats the case. I would reccommend tying or penning him so he can't go anywhere else until you find out what's wrong.